Fix PS5 test failure: only mock Test-Json on PS7+ where it exists

Author: Copilot

Tests/ReadSettings.Test.ps1

@@ -543,19 +543,18 @@ InModuleScope ReadSettings { # Allows testing of private functions
 
         It 'ValidateSettings skips validation entirely on PS versions less than 7 without warning' {
             Mock OutputWarning { }
-            Mock Test-Json { }
 
             $settings = @{ "someProp" = "someValue" }
 
-            ValidateSettings -settings $settings
-
             if ($PSVersionTable.PSVersion.Major -ge 7) {
+                Mock Test-Json { }
+                ValidateSettings -settings $settings
                 # On PS7+, Test-Json is called directly for validation
                 Should -Invoke -CommandName Test-Json -Times 1
             }
             else {
-                # On PS < 7, validation is skipped entirely
-                Should -Invoke -CommandName Test-Json -Times 0
+                # On PS < 7, validation is skipped entirely; Test-Json doesn't exist so we just verify no warning
+                ValidateSettings -settings $settings
             }
 
             # Verify no warning was output